Vibration-type driving device, control apparatus for controlling the driving of the vibration-type driving device, and electronic equipment having the vibration-type driving device and the control apparatus

ABSTRACT

A vibration-type driving device comprises a vibration element including a driving member and an electro-mechanical energy conversion element having an electrode and arranged to displace the driving member with a driving signal supplied to the electrode, and a driven element that is kept in contact with the driving member of the vibration element. According to the driving signal supplied to the electrode of the electro-mechanical energy conversion element, the vibration element excites vibrations in two flexural vibration modes in which a direction of generation of a node in one mode is perpendicular to that in the other mode. With the use of the two flexural vibration modes, the natural vibration frequency of the vibration element can be prevented from increasing, and the position of a node occurring in one flexural vibration mode and the position of an antinode occurring in the other flexural vibration mode can be made to coincide with each other, so that the amount of displacement of the driving member can be made large.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 10/804,343, filedMar. 19, 2004, which claims the benefit of Japanese Application2003-092783, filed Mar. 28, 2003, and Japanese Application 2003-108325,filed Apr. 11, 2003, the entire contents of which are incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vibration-type driving device havinga vibration element and a driven element, and more particularly to thestructural arrangement of the vibration element.

2. Description of Related Art

Various conventional ultrasonic actuators for linear motion include aflat-plate-like vibration element. U.S. Pat. No. 5,698,930, for example,discloses such an ultrasonic actuator, which has an elastic body formedas a flat-plate-like vibration element. Vibrations can occur in theflat-plate-like vibration element in both a longitudinal vibration(oscillation) mode and flexural vibration mode. Also, displacementmotions caused by vibrations in these modes are combined with each otherto generate an elliptical movement or circular movement.

Another element (member) known as the driven element is kept in contactwith the plate-like vibration element to cause relative movement betweenboth elements.

Another example of an ultrasonic actuator with a flat-plate-likevibration element is disclosed in Japanese Laid-Open Patent ApplicationNo. Hei 6-311765. Here, the flat-plate-like vibration element is excitedin two flexural vibrations. The structural arrangement of that vibrationelement is described with reference to FIGS. 35A, 35B and 35C.

In FIG. 35A, there is shown a flat-plate-like elastic body 100. Apiezoelectric element 101 is bonded to one surface of the elastic body100. Vibrations occur in a first flexural vibration mode, the behaviorof which is shown in FIG. 35B, and in a second (out-of-plane) flexuralvibration mode, the behavior of which is shown in FIG. 35C.

The behavior of vibration shown in FIG. 35B indicates that the firstflexural vibration mode has cross-like nodes X₁ and Y₁, in whichvibratory displacement motions in the Z direction are caused atprotruding portions 102 a, 102 b, 102 c and 102 d. The behavior ofvibration shown in FIG. 35C indicates that the second, out-of-planeflexural vibration mode has two nodes X₂ and X₃ in the Y direction, inwhich vibratory displacement motions in the X direction are caused atthe protruding portions 102 a to 102 d.

In FIG. 35A, the driven element (an element to be driven), not shown, isdisposed on contact portions 105 a, 105 b, 105 c and 105 d, on the tipsof the protruding portions 102 a to 102 d. The driven element is kept inpressure contact with the contact portions 105 a to 105 d.

Vibratory displacement motions caused by the first and second flexuralvibrations are combined with each other, so that an elliptical movementcan be generated within the X-Z plane on the tips of the protrudingportions 102 a to 102 d. Accordingly, the vibration element and thedriven element can be moved relative to each other.

However, there are disadvantages associated with the above-describedconventional vibration-type driving devices. In the first type (U.S.Pat. No. 5,698,930), which excites flexural vibration and longitudinalvibration, vibrations are excited at the plate-like elastic body in alongitudinal-vibration primary mode, so that it is difficult to reducethe size of the plate-like vibration element because an increasedresonance frequency can result. Correspondingly, the vibration amplitudeof the elliptical movement cannot be enlarged. This can cause drivingperformance to fluctuate in individual driving devices.

In the second type, which excites two flexural vibrations, vibrationsare excited at the plate-like elastic body in the second, out-of-planeflexural vibration mode of FIG. 35C, so that there is an advantage inreducing the size of the elastic body. However, in the first vibrationmode of FIG. 35B, cross-like nodes occur in this flexural vibrationmode, so that the distribution of strains becomes complicated.Accordingly, some measures are required to excite such vibrations.

Further, the protruding portions 102 a to 102 d are distant frompositions that cause the maximum amount of displacement in the Zdirection in the flexural vibration mode shown in FIG. 35B. Therefore,it is difficult to provide sufficient amount of vibratory displacementto the protruding portions 102 a to 102 d, and to exert a larger drivingforce on the driven element.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a vibration-typedriving device is disclosed. The vibration-type driving device has avibration element which further includes a driving member and anelectro-mechanical energy conversion element having an electrode. Theelectro-mechanical energy conversion element uses a driving signalsupplied to the electrode to displace the driving member. Thevibration-type device further includes a driven element in contact withthe driving member. Using the driving signal, the vibration elementexcites vibrations in two flexural vibration modes in which a directionof generation of a node in one mode is not parallel to that in the othermode. For example, the direction of generation of a node in one mode maybe perpendicular to the direction of generation of a node in the othermode.

With the vibration-type driving device configured as mentioned above, itis possible to prevent a natural vibration frequency of the vibrationelement from increasing, and it is also possible to make the position ofa node occurring in one flexural vibration mode and the position of anantinode occurring in the other flexural vibration mode coincide witheach other.

In accordance with another aspect of the present invention, there isprovided a vibration-type driving device comprising a vibration elementincluding an elastic body and an electro-mechanical energy conversionelement having at least two electrodes and arranged to cause the elasticbody to excite vibrations with two driving voltages of respective phaseshaving the same frequency applied to the two electrodes, and a drivenelement that is kept in contact with the elastic body, wherein thevibration element is capable of forming a first flexural vibration modein response to inputting of the two driving voltages of respectivephases that are made the same and is capable of forming a secondflexural vibration mode in response to inputting of the two drivingvoltages of respective phases that are made opposite to each other, andwherein the first flexural vibration mode and the second flexuralvibration mode are combined to drive the vibration element and thedriven element relative to each other.

With the vibration-type driving device configured as mentioned above, itis possible to make the electrode pattern of the electro-mechanicalenergy conversion element have simpler arrangement.

In accordance with a further aspect of the present invention, there isprovided a control apparatus comprising an arithmetic circuit forcontrolling the vibration-type driving device.

The above and further aspects, features and advantages of the presentinvention will become apparent to those skilled in the art upon readingof the following detailed description of preferred embodiments thereofwhen taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are perspective views showing a vibration-type drivingdevice according to a first embodiment of the invention.

FIGS. 2A and 2B are diagrams illustrating vibration modes of a vibrationelement of the first embodiment.

FIGS. 3A and 3B are diagrams showing the structural arrangement of amulti-layer piezoelectric element of the first embodiment.

FIG. 4 is a diagram showing the electrical connection state of thevibration element of the first embodiment.

FIG. 5 is a perspective view showing an alternative form of vibrationelement of the first embodiment.

FIGS. 6A and 6B are diagrams illustrating vibration modes of thealternative form of vibration element of the first embodiment.

FIGS. 7A and 7B are diagrams showing examples of modification of thefirst embodiment.

FIG. 8 is a perspective view showing a vibration-type driving deviceaccording to a second embodiment of the invention.

FIGS. 9A and 9B are diagrams showing the structural arrangement of amulti-layer piezoelectric element of the second embodiment.

FIG. 10 is a diagram showing the electrical connection state of thevibration element of the second embodiment.

FIG. 11 is a diagram showing the structural arrangement of apiezoelectric element of a third embodiment of the invention.

FIG. 12 is a diagram showing a multi-layer piezoelectric element as analternative form of piezoelectric element of the third embodiment.

FIG. 13 is a diagram showing the electrical connection state of themulti-layer piezoelectric element as the alternative form ofpiezoelectric element of the third embodiment.

FIGS. 14A and 14B are diagrams showing the structural arrangement of amulti-layer piezoelectric element of a fourth embodiment of theinvention.

FIG. 15 is a perspective view showing a vibration element of a fifthembodiment of the invention.

FIGS. 16A and 16B are diagrams illustrating vibration modes of avibration element of the fifth embodiment.

FIG. 17 is a diagram showing the structural arrangement of apiezoelectric element of the fifth embodiment.

FIG. 18 is a perspective view showing a vibration element of a sixthembodiment of the invention.

FIGS. 19A and 19B are diagrams illustrating vibration modes of thevibration element of the sixth embodiment.

FIG. 20 is a perspective view showing a vibration-type driving deviceaccording to the sixth embodiment.

FIG. 21 is a diagram showing the electrode pattern of a piezoelectricelement of the sixth embodiment.

FIG. 22 is a diagram showing, with vectors, the relationship betweenvoltages applied to the piezoelectric element and the vibration modes.

FIG. 23 is a perspective view showing a vibration-type driving device asan example of modification of the sixth embodiment.

FIGS. 24A and 24B are diagrams illustrating vibration modes of thevibration element of the vibration-type driving device shown in FIG. 23.

FIG. 25 is a perspective view showing a vibration-type driving device asanother example of modification of the sixth embodiment.

FIGS. 26A and 26B are diagrams illustrating vibration modes of thevibration element of the vibration-type driving device shown in FIG. 25.

FIG. 27 is a diagram showing the mechanism of a lens unit according to aseventh embodiment of the invention.

FIG. 28 is a block diagram illustrating a control apparatus of theseventh embodiment.

FIG. 29 is a diagram showing the relationship between the phasedifference of applied voltages and the vibration amplitude of theseventh embodiment.

FIG. 30 is a diagram showing the relationship between the drivingfrequency and the driving speed of a vibration-type driving device ofthe seventh embodiment.

FIGS. 31A and 31B are diagrams for explaining an elliptical movement ofprotruding portions of the vibration-type driving device of the seventhembodiment.

FIGS. 32A and 32B are diagrams for explaining an elliptical movement ofprotruding portions of a vibration-type driving device according to aneighth embodiment of the invention.

FIG. 33 is a block diagram illustrating a control apparatus of theeighth embodiment.

FIG. 34 is a diagram showing the relationship between the phasedifference of applied voltages and the vibration amplitude of the eighthembodiment.

FIGS. 35A, 35B and 35C are perspective views showing a vibration elementaccording to the related art.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in detail withreference to the drawings.

(First Embodiment)

FIGS. 1A and 1B are perspective views showing the appearance of alinear-type ultrasonic actuator 10 serving as a vibration-type drivingdevice according to a first embodiment of the invention.

In FIG. 1A, the linear-type ultrasonic actuator 10 is composed of avibration element 1 and a linear slider 6.

The vibration element 1 is composed of a multi-layer piezoelectricelement 5 formed into a rectangular thin-plate shape, and a drivingplate 2 made of an elastic body and bonded integrally to one end surfaceof the multi-layer piezoelectric element 5. The multi-layerpiezoelectric element 5 also has a plurality of thin-plate-likepiezoelectric element films each having electrodes on the front surfacethereof. The multi-layer piezoelectric element 5 is anelectro-mechanical energy conversion element in which mechanicaldisplacement occurs in response to an electrical signal being suppliedthereto. Preferably, the size of the multi-layer piezoelectric element 5may be approximately 10×6×0.6 (mm).

The driving plate 2 has a plate portion formed into a rectangular shape,and two protruding portions 3-1 and 3-2 each formed into a protrusiveshape on the top surface of the plate portion. On the tip surfaces ofthe protruding portions 3-1 and 3-2, there are formed contact portions4-1 and 4-2, which are arranged to be kept in contact with the linearslider 6, which is a driven element. Thus, the protruding portions 3-1and 3-2 are kept in contact with the linear slider 6 and then act as adriving member for moving the linear slider 6 relative to the vibrationelement 1.

Stainless steel, which excels in vibration characteristics, is used forthe driving plate material. The stainless steel is also heat-treatedsince the contact portions 4-1 and 4-2 require good a friction factor,abrasion resistance, or the like.

It should be noted that the material of the driving plate 2 is notlimited to stainless steel and may be another metal as in conventionalvibration-type driving devices.

The protruding portions 3-1 and 3-2 are formed integrally with thedriving plate 2 by means of press working or the like. Here, theprotruding portions 3-1 and 3-2 and the driving plate 2 may be formedseparately and then fixed to each other, but the integral formationthereof can produce such advantageous effects that it is possible toreduce the number of required parts and cost, it is possible to increasethe assembly productivity of devices because of a reduction in thenumber of steps of assembly work, and it is possible to preventprecision fluctuations in individual parts because of positioning ofparts being unnecessary.

FIG. 1B illustrates the structural arrangement for supporting thevibration element 1. As shown in FIG. 1B, a multi-layer piezoelectricelement 5 is fixed to a printed circuit board 7, which supplies adriving signal (a driving voltage) to the multi-layer piezoelectricelement 5. Also shown is a stationary member 8 fixed to an apparatus soas to mount the ultrasonic actuator 10 thereon. A support member 9mounts the vibration element 1 on the stationary member 8 to allowvibration of the vibration element 1 and is arranged to bring thevibration element 1 into pressure contact with the slider 6. Althoughnot shown, other structural members can be employed for supporting thevibration element 1, which may include fixing means for fixing thevibration element 1 in such a manner as not to hider the vibrationthereof, means for bringing the vibration element and the driven elementinto pressure contact with each other, and means for supplying a drivingsignal to the piezoelectric element. Hereinafter, for the purpose ofsimplification, the printed circuit board 7, the stationary member 8 andthe support member 9 will be omitted from the description of thestructural arrangement of the vibration element 1. Note that anexemplary size of the vibration element 1 including the protrudingportions 3-1 and 3-2 is 10×6×2 (mm).

FIGS. 2A and 2B show the shapes of the vibration element 1 occurring intwo vibration modes (MODE-A and MODE-B). Each vibration mode is aflexural vibration mode in which the plate-like vibration element 1 isflexed in an out-of-plane direction. These two modes (MODE-A and MODE-B)will be described with reference to the X, Y and Z coordinate system.

The shape of the vibration element 1 is determined in advance so as tomake the resonance frequencies in the two vibration modes approximatelycoincide with each other. The resonance frequency of the vibrationelement 1 shown in FIGS. 2A and 2B is about 80 kHz. FIG. 2A is a view ofthe vibration element 1 as seen from the Y direction. When the vibrationelement 1 is excited in MODE-A, nodes (α) of vibration appear at threepoints or lines (secondary flexural vibration mode) as shown in thelower half of FIG. 2A. These nodes extend in the Y direction of thevibration element 1.

In MODE-A, when the vibration element 1 is seen from the X direction, nonodes of vibration appear. The protruding portions 3-1 and 3-2 aredisposed at or in the vicinity of positions where nodes occur in thevibration in MODE-A, as shown in FIG. 2A. Accordingly, the vibration inMODE-A causes the contact portions 4-1 and 4-2 to make a reciprocatingmotion in the X direction as indicated by arrows in FIG. 2A.

Thus, since the protruding portions 3-1 and 3-2 are disposed at or inthe vicinity of positions of nodes in MODE-A, the protruding portions3-1 and 3-2 can be displaced to the greatest extent in the X direction.

FIG. 2B is a view of the vibration element 1 as seen from the Xdirection. When the vibration element 1 is excited in MODE-B, nodes (β)of vibration appear at two points or lines (primary flexural vibrationmode) as shown in the lower half of FIG. 2B. These nodes extend in the Xdirection of the vibration element 1. In other words, a group of nodesof the vibration in MODE-A and a group of nodes of the vibration inMODE-B are not in parallel with each other and are, instead,perpendicular to each other within the X-Y plane. In MODE-B, when thevibration element 1 is seen from the Y direction, no nodes of vibrationappear.

The protruding portions 3-1 and 3-2 are disposed at or in the vicinityof positions where antinodes occur in the vibration in MODE-B, as shownin FIG. 2B. Accordingly, the vibration in MODE-B causes the contactportions 4-1 and 4-2 to make a reciprocating motion in the Z directionas indicated by arrows in FIG. 2B.

Thus, since the protruding portions 3-1 and 3-2 are disposed at or inthe vicinity of positions of antinodes in MODE-B, the protrudingportions 3-1 and 3-2 can be displaced to the greatest extent in the Zdirection. As mentioned above, the protruding portions 3-1 and 3-2 aredisplaced to a great degree in both the X direction and the Z direction,so that it is possible to exert a large driving force on the linearslider 6.

When an intended driving signal is supplied to the multi-layerpiezoelectric element 5, the above-described vibration modes (MODE-A andMODE-B) are caused in the vibration element 1 owing to inversepiezoelectric effect. Then, vibrations are excited in such a manner thatthe phase difference between vibrations in MODE-A and MODE-B becomes 90°or approximately 90°, so that an elliptical movement within the X-Zplane shown in FIG. 1A is generated at the contact portions 4-1 and 4-2.Accordingly, the linear slider 6 is moved in the X direction so that itis pushed by the contact portions 4-1 and 4-2 where the ellipticalmovement is generated.

Here, strains that take place in the vibration element 1 when theabove-described vibration modes (MODE-A and MODE-B) are caused will bedescribed.

First, in the case of MODE-A, characters (+) and (−) shown in FIGS. 2Aand 2B represent the signs of strain components in the X direction thattake place when deformation is caused by vibrations in the vibrationelement 1. The character (+) indicates that the multi-layerpiezoelectric element 5 has expanded in the X direction, and thecharacter (−) indicates that the multi-layer piezoelectric element 5 hascontracted in the X direction.

With the characters (+) and (−) taken into consideration, themulti-layer piezoelectric element 5 is divided into two regions in thethickness direction (Z direction) with the boundary formed by a neutralplane T1 where no strains in the X direction take place. Further, thesigns of the characters (+) and (−) reverse across the vicinity of thecenter of the multi-layer piezoelectric element 5 in the X direction(see FIG. 2A).

In the case of MODE-B, if the signs of strain components in the Ydirection that take place in the multi-layer piezoelectric element 5 aretaken into consideration, the multi-layer piezoelectric element 5 isdivided into two regions in the thickness direction (Z direction) withthe boundary formed by a neutral plane T2 where no strains in the Ydirection take place (see FIG. 2B).

FIG. 3A is a schematic diagram showing the layered structure of themulti-layer piezoelectric element 5. The multi-layer piezoelectricelement 5 employed in the first embodiment is formed with an exemplarynumber of ten piezoelectric element films L (L1 to L10) joined one uponanother.

Since an exemplary thickness of each piezoelectric element film is about0.06 mm, the thickness of the multi-layer piezoelectric element 5 isabout 0.6 mm. On the front surface of each of the piezoelectric elementfilms L2 to L10, there are formed electrode films P1 to P4 as shown inFIG. 3A. Also, there are formed via-hole electrodes H1 to H4 piercingthe piezoelectric element films to make conduction with electrode filmsformed on the upper and lower layers.

On each of the even-numbered piezoelectric element films L2, L4, L6, L8and L10 among the piezoelectric element films L2 to L10, there areformed two electrode films P1 and P2, which are approximately symmetricin the X direction in FIG. 3A. Similarly, on each of the odd-numberedpiezoelectric element films L3, L5, L7 and L9 among the piezoelectricelement films L3 to L9, there are formed two electrode films P3 and P4,which are approximately symmetric in the X direction in FIG. 3A.

The electrode film P1 is electrically connected to the via-holeelectrode H1. Similarly, the electrode film P2 is electrically connectedto the via-hole electrode H2, the electrode film P3 to the via-holeelectrode H3, and the electrode film P4 to the via-hole electrode H4. Onthe piezoelectric element film L1 forming the front surface of themulti-layer piezoelectric element 5, there are formed four via-holeelectrodes H1 to H4. The via-hole electrodes H1 to H4 function to makeconduction with the electrode films formed on the piezoelectric elementfilm L2 and subsequent piezoelectric element films as well as externalterminals.

Characters (+) and (GND) shown in FIG. 3A represent electric potentialsappearing at the time of polarization. For example, the region of theelectrode film P1 of the piezoelectric element film L2 is made topolarize in the thickness direction (Z direction) by the potentialbetween the electrode film P1 and the electrode film P3 formed on thepiezoelectric element film L3. Also, the region of the electrode film P2of the piezoelectric element film L2 is polarized in the thicknessdirection (Z direction) using the potential between the electrode filmP2 and the electrode film P4 formed on the piezoelectric element filmL3. Similarly, each of the piezoelectric element films L3 to L9 ispolarized in the thickness direction (Z direction) by the potentialbetween the associated electrode films.

In FIG. 3B, there is schematically shown the polarized state of themulti-layer piezoelectric element 5 corresponding to the situation whena potential is applied to the via-hole electrode H1 with the via-holeelectrode H3 exposed on the front surface of the multi-layerpiezoelectric element 5 as a common potential and when a potential isapplied to the via-hole electrode H2 with the via-hole electrode H4 as acommon potential. Thus, as shown in FIGS. 3A and 3B, the multi-layerpiezoelectric element 5 is divided into two regions that areapproximately symmetric in the X direction. Also, correspondingly withthe two regions, the multi-layer piezoelectric element 5 has areas R1and R2 that are polarized in the same direction when seen in thethickness direction (Z direction).

FIG. 4 shows the bottom surface of the vibration element 1. This bottomsurface includes the front surface of the multi-layer piezoelectricelement 5, which has terminal electrodes H1 to H4. The terminalelectrodes H1 to H4 serve also as via-hole electrodes that are formed onthe piezoelectric element film L1.

In FIG. 4, a potential V1 is applied to the terminal electrode H1.Similarly, a potential V2 to the terminal electrode H2, a potential V3to the terminal electrode H3, and a potential V4 to the terminalelectrode H4. It is now assumed that the difference between thepotential V1 and the potential V3 is a potential difference E1 and thedifference between the potential V2 and the potential V4 is a potentialdifference E2. Here, the individual potentials V1 to V4 are determinedin such a way that the potential differences E1 and E2 becomealternating signals in the vicinity of resonance frequencies in MODE-Aand MODE-B. Moreover, the individual potentials V1 to V4 are determinedin such a way that the levels of signals of the potential differences E1and E2 become the same.

While the areas R1 and R2 are polarized in the same direction, they maybe polarized in opposite directions so as to make it possible to performthe driving of the ultrasonic actuator with the same construction asthat described above.

Further, while, in the first embodiment, a single multi-layerpiezoelectric element 5 is used as a piezoelectric element of thevibration element 1, a plurality of piezoelectric elements may be usedto obtain the same function as that of the multi-layer piezoelectricelement 5. In addition, the areas R1 and R2 may be formed with therespective individual multi-layer piezoelectric elements.

In summary, in the ultrasonic actuator according to the firstembodiment, two flexural vibration modes (MODE-A and MODE-B) in whichthe direction of generation of a node in MODE-A is approximatelyperpendicular to that in MODE-B and in which the respective frequenciesare approximately coincident with each other are combined to generate anelliptical movement at the protruding portions 3-1 and 3-2 (the contactportions 4-1 and 4-2).

With the two flexural vibration modes, the size of the vibration elementcan be reduced without increasing the driving frequency. Then, with thereduction in size of the vibration element, the size of the ultrasonicactuator can be reduced.

On the other hand, the multi-layer piezoelectric element 5, which iscomposed of a plurality of piezoelectric element films, is used as apiezoelectric element for exciting vibrations in the vibration element,so that the construction of the piezoelectric element that is suitablefor the vibration excitation in vibration element can be realized. Thedriving signal level can also be kept low as compared with the casewhere a single piezoelectric element is used.

Further, the multi-layer piezoelectric element 5 is divided into tworegions that are approximately symmetric in a predetermined direction(the X direction), and the two regions are made to function forexcitation in two vibration modes, so that the multi-layer piezoelectricelement can have a simple construction. As a result, the whole region ofthe piezoelectric element can participate in driving the driven element,and any region of the piezoelectric element that is not involved indriving the driven element is eliminated, so that a sufficient outputpower can be obtained despite the small-sized vibration element beingused.

In other words, even when the vibration element is reduced in size, asufficient output power to drive the driven element can be obtained, anda vibration element that excels in output characteristic can berealized. On the other hand, if the vibration element is kept in anordinary size, the vibration element can produce a larger output power.

Thus, even in an ultrasonic actuator serving as a vibration-type drivingdevice that uses the above-described vibration element, a larger outputpower can be obtained regardless of size.

It should be noted that the construction of the vibration element is notlimited to that of the vibration element 1 as described in the firstembodiment. For example, such an ultrasonic actuator 10 as shown in FIG.5 is attainable.

In FIG. 5, in an approximately central position on the top surface ofthe vibration element 1, there is formed one protruding portion 3-1.Also, on the tip of the protruding portion 3-1, there is formed acontact portion 4-1, which is kept in contact with the linear slider 6.The other structural arrangement is similar to that described in thefirst embodiment (FIG. 1A).

With the vibration modes (MODE-A and MODE-B) and the multi-layerpiezoelectric element 5 used, states of vibration as shown in FIGS. 6Aand 6B are obtained. A position where the protruding portion 3-1 isformed is the position of a node in MODE-A as well as the position of anantinode in MODE-B. Accordingly, at the contact portion 4-1 of theprotruding portion 3-1, a reciprocating motion in the X direction asindicated by arrows in FIG. 6A is generated by the vibration in MODE-A.Also, at the contact portion 4-1, a reciprocating motion in the Zdirection as indicated by arrows in FIG. 6B is generated by thevibration in MODE-B.

The thus-generated motions in the Z direction and Y direction cause thecontact portion 4-1 to make an elliptical movement, thereby causing thelinear slider 6 and the vibration element 1 to move relative to eachother.

Since, as shown in FIG. 5, a single protruding portion 3-1 is formed onthe vibration element 1, it is viable to shorten (reduce in size) thelinear slider 6, which is kept in contact with the protruding portion3-1. Then, with the linear slider 6 reduced in size, it is viable tofurther reduce the size of the ultrasonic actuator 10.

In the first embodiment, MODE-A is made to be an out-of-plane secondaryflexural vibration mode, and MODE-B is made to be an out-of-planeprimary flexural vibration mode.

The driving plate 2 of the vibration element 1, which is rectangular inshape, is approximately symmetric with respect to a plane passingthrough the center of the driving plate 2 and extending in the Xdirection or the Y direction (see FIG. 1A). Accordingly, the anode andantinode in MODE-A and MODE-B are generated at positions that aresymmetric with respect to the above-mentioned plane in the vibrationelement 1, as shown in FIGS. 2A and 2B.

Consequently, two protruding portions 3-1 and 3-2 can be formed atapproximately symmetric positions on the vibration element 1, as shownin FIG. 1A. Also, a single protruding portion 3-1 can be formed in thevicinity of the central position of the vibration element 1, as shown inFIG. 5. Even so, the single protruding portion 3-1 becomes symmetricwith respect to the above-mentioned plane.

With the protruding portions 3-1 and 3-2 disposed as described above,the vibration element 1 can impartially receive a reaction force fromthe linear slider 6 at the protruding portions 3-1 and 3-2. Further,since the positional relationship between the linear slider 6 and thecontact portions 4-1 and 4-2 becomes stable, it is possible to realize avibration-type driving device capable of generating a stable outputpower without being influenced by environmental or other such changes.

Moreover, in the first embodiment as described above, the linear slider6 for linear motion is employed as a driven element in the ultrasonicactuator 10. However, the driven element according to the inventionshould not be limited the linear slider 6. More specifically, a memberformed in the shape of cylinder, disc, ellipse or the like may beemployed as the driven element, and such a member may be caused to makea rotary movement.

The structural arrangement of an ultrasonic actuator 10 for producingsuch a rotary movement is shown in FIGS. 7A and 7B. In FIGS. 7A and 7B,a vibration element 1 similar to that of the first embodiment isemployed, and a disc-shaped rotor 30 (see FIG. 7A) or a ring-shapedrotor 31 (see FIG. 7B) is brought into contact with the vibrationelement 1 so as to complete the ultrasonic actuator 10.

With the structural arrangement of the ultrasonic actuator 10 asdescribed above, the rotor 30 or 31 makes a rotary movement indirections indicated by arrows shown in FIGS. 7A and 7B.

(Second Embodiment)

FIG. 8 is a perspective view showing the appearance of a linear-typeultrasonic actuator 10 serving as a vibration-type driving deviceaccording to a second embodiment of the invention.

In FIG. 8, the vibration element 1 is composed of a multi-layerpiezoelectric element 5 formed into a rectangular thin-plate shape, andtwo protruding portions 3-1 and 3-2 formed integrally with themulti-layer piezoelectric element 5 on the front surface thereof. On thetip surfaces of the protruding portions 3-1 and 3-2, there are formedcontact portions 4-1 and 4-2, which are kept in contact with a linearslider 6 serving as a driven element.

Thus, while, in the first embodiment, the multi-layer piezoelectricelement 5, the driving plate 2 and the protruding portions 3-1 and 3-2constitute the vibration element 1, the multi-layer piezoelectricelement 5 and the protruding portions 3-1 and 3-2 constitute thevibration element 1 in the second embodiment.

The protruding portions 3-1 and 3-2 are required to have properties thatexcel in friction factor or abrasion resistance, and, in the secondembodiment, alumina is used as the material of the protruding portions3-1 and 3-2. Two vibration modes (MODE-A and MODE-B) to be caused in thevibration element 1 in the second embodiment are the same as thosedescribed in the first embodiment (see FIGS. 2A and 2B).

FIGS. 9A and 9B are schematic diagrams showing the layered structure ofthe multi-layer piezoelectric element 5 in the second embodiment. Themulti-layer piezoelectric element 5 is formed with an exemplary numberof twelve piezoelectric element films L (L1 to L12) joined one uponanother. Since the thickness (exemplary) of each piezoelectric elementfilm is about 0.06 mm, the thickness of the multi-layer piezoelectricelement 5 is about 0.72 mm.

In FIG. 9A, on the front surfaces of the piezoelectric element films L2to L12, there are formed electrode films P1 to P6, which are dividedinto two groups that are approximately symmetric in the X direction. Oneach of the piezoelectric element films L2, L4 and L6, there are formedelectrode films P1 and P2, and on each of the piezoelectric elementfilms L8, L10 and L12, there are formed electrode films P5 and P6. Onthe odd-numbered piezoelectric element films L3, L5, L7, 19 and L11among the piezoelectric element films L3 to L11, there are formedelectrode films P3 and P4.

The electrode films P1 to P6 are electrically connected to via-holeelectrodes H1 to H6, respectively. More specifically, the electrode filmP1 is electrically connected to the via-hole electrode H1, the electrodefilm P2 to the via-hole electrode H2, the electrode film P3 to thevia-hole electrode H3, the electrode film P4 to the via-hole electrodeH4, the electrode film P5 to the via-hole electrode H5, and theelectrode film P6 to the via-hole electrode H6.

Via-hole electrodes H1 to H6 that are formed on the piezoelectricelement film L1 serve as terminal electrodes that are used to conductelectrical connection between the multi-layer piezoelectric element 5and the outside. When the terminal electrodes H1 and H2 are given apositive potential, the terminal electrodes H3 and H4 are given anegative potential, and the terminal electrodes H5 and H6 are given acommon potential, such polarization as indicated by characters (+), (−)and (GND) in FIG. 9A is caused.

FIG. 9B schematically shows the directions of polarization inside themulti-layer piezoelectric element 5. As shown in FIG. 9B, areas R1 andR2 are formed in the range of the piezoelectric element films L2 to L6,and areas R3 and R4 are formed in the range of the piezoelectric elementfilms L7 to L11.

The action of the multi-layer piezoelectric element 5, which is part ofthe vibration element 1 is as follows.

The areas R1 and R2 of the multi-layer piezoelectric element 5 arelocated above the neutral planes T1 and T2 shown in FIGS. 2A and 2B, andthe areas R3 and R4 are located below the neutral planes T1 and T2.

As shown in FIG. 10, electrical potentials V1 to V4 are applied to theterminal electrodes H1 to H6, which are formed on the front surface ofthe multi-layer piezoelectric element 5. More specifically, thepotential V1 is applied to the terminal electrodes H1 and H5. Thepotential V3 is applied to the terminal electrode H3. It is now assumedthat the potential difference between the potentials V1 and V3 is apotential difference E1.

When potentials having the potential difference E1 are applied to themulti-layer piezoelectric element 5, the areas R1 and R3 have propertiesin opposite directions with respect to polarization and potentialdifference, for example, a strain for expansion is generated in the areaR1 and, at the same time, a strain for contraction is generated in thearea R3. In other words, the multi-layer piezoelectric element 5functions like a bimorph with the areas R1 and R3 paired.

On the other hand, the potential V2 is applied to the terminalelectrodes H2 and H6, and the potential V4 is applied to the terminalelectrode H4. It is now assumed that the potential difference betweenthe potentials V2 and V4 is a potential difference E2.

When potentials having the potential difference E2 are applied to themulti-layer piezoelectric element 5, for example, a strain for expansionis generated in the area R2 and, at the same time, a strain forcontraction is generated in the area R4. In other words, the multi-layerpiezoelectric element 5 functions like a bimorph with the areas R2 andR4 paired.

In the vibration element 1 that uses the multi-layer piezoelectricelement 5 having the above-described structural arrangement, vibrationsare made to be generated in almost the whole region of portions thatconstitute the vibration element 1.

According to the second embodiment, the use of the multi-layerpiezoelectric element 5 makes it viable to obtain a sufficient outputpower despite the voltage level of the driving signal being low ascompared with the case where a single piezoelectric element is used, andalso makes it viable to realize a small-sized and high-powervibration-type driving device.

(Third Embodiment)

FIG. 11 shows the structural arrangement of a piezoelectric element 5 ina linear-type ultrasonic actuator serving as a vibration-type drivingdevice according to a third embodiment of the invention. In the thirdembodiment, the driving plate 2, the protruding portions 3-1 and 3-2 andthe ultrasonic actuator 10 are the same in construction as thosedescribed in the first embodiment (FIG. 1A), but the construction of apiezoelectric element in the ultrasonic actuator 10 is different fromthat described in the first embodiment.

As shown in FIG. 11, on one end surface of the piezoelectric element 5,there are formed five electrode films P1 to P5, which are arranged to beapproximately symmetric both in the X direction and the Y direction. Theelectrode films P1 and P2 as well as the electrode films P3 and P4 arearranged to be approximately symmetric with respect to the X-axispassing through the center of the piezoelectric element 5.

Also, the electrode films P1 and P3 as well as the electrode films P2and P4 are arranged to be approximately symmetric with respect to theY-axis passing through the center of the piezoelectric element 5.

Further, on a region passing through the vicinity of the center of thepiezoelectric element 5 and extending in the X direction, there isformed an electrode film P5. It is now assumed that, in thepiezoelectric element 5, parts surrounded with the electrode films P1 toP5 as mentioned above and the common electrode formed on the back sideof the piezoelectric element 5 (i.e., areas extending in the Z directionfrom the electrode films P1 to P5) are areas R1 to R5, respectively.

In the areas R1 to R5, polarization is caused as indicated by characters(+) and (−) in FIG. 11. With the above-mentioned piezoelectric element 5incorporated in the vibration element 1, when a common driving signal issupplied to the electrode films P1 to P4, strains in opposite directionsare generated in the areas R1, R2 and the areas R3, R4.

Then, such deformation of the piezoelectric element 5 causes vibrationsthereof in MODE-A as described in the first embodiment. When anotherdriving signal is supplied to the electrode film P5, the vibration inMODE-B as described in the first embodiment is caused.

In each of the areas R1 to R5, for example, the width thereof in the Ydirection can be arbitrarily determined in accordance with design. Withsuch determination, an output power to be generated in two vibrationmodes (MODE-A and MODE-B) can be determined, so that the shape of anelliptical movement to be generated in the vibration element 1 iscontrollable. As a result, it is possible to realize an ultrasonicactuator that excels in efficiency of driving.

In the third embodiment, a multi-layer piezoelectric element may be usedas the piezoelectric element 5. Such a modification of the thirdembodiment is described with reference to FIG. 12, which shows theconstruction of the multi-layer piezoelectric element 5. Here, theconstruction using piezoelectric element films, electrode films andvia-hole electrodes is the same as that described in the precedingembodiments, and, therefore, the detailed description thereof isomitted.

The multi-layer piezoelectric element 5 is composed of ten layers ofelectrode films, i.e., piezoelectric element films L1 to L10. On each ofthe even-numbered piezoelectric element films L2, L4, L6, L8 and L10among the piezoelectric element films L2 to L10, there are formed fiveelectrode films P1 to P5. Also, on each of the odd-numberedpiezoelectric element films L3, L5, L7 and L9 among the piezoelectricelement films L3 to L9, there is formed one electrode film P6, whichcovers almost the whole surface of each piezoelectric element film.

Each piezoelectric element film is surrounded by the electrode films P1to P5 and the electrode film P6, and portions corresponding to theassociated electrode films function as individual driving areas. It isnow assumed that such areas corresponding to the electrode films P1 toP5 are areas R1 to R5, respectively. These areas R1 to R5 are arrangedin the same way as in the piezoelectric element shown in FIG. 11.

When a potential is applied to the areas R1 to R4, the vibration inMODE-A as described in the first embodiment is excited, and, when apotential is applied to the area R5, the vibration in MODE-B asdescribed in the first embodiment is excited.

The electrical conduction between the multi-layer piezoelectric element5 in the modification of the third embodiment and the outside iseffected in such a manner as shown schematically in FIG. 13. Morespecifically, a potential V1 is applied to the terminal electrodes H1 toH4, a potential V2 is applied to the terminal electrode H5, and apotential VG is applied to the terminal electrode H6. The terminalelectrodes H1 to H6 function also as via-hole electrodes H1 to H6,respectively, formed on the piezoelectric element films L1 to L10.

Thus, the areas R1 to R4 are given a potential difference E1 between thepotential V1 and the potential VG, and the area R5 is given a potentialdifference E2 between the potential V2 and the potential VG. With themulti-layer piezoelectric element 5 and the driving signals arranged asdescribed above, the vibration in MODE-A is excited by the areas R1 toR4, and the vibration in MODE-B is excited by the area R5, in the sameway as described with reference to FIG. 11.

(Fourth Embodiment)

FIGS. 14A and 14B show the structural arrangement of a multi-layerpiezoelectric element 5 in a linear-type ultrasonic actuator serving asa vibration-type driving device according to a fourth embodiment of theinvention. Here, the vibration element 1 and the ultrasonic actuator 10are the same in construction as those described in the second embodiment(FIG. 8), and, therefore, the detailed description thereof is omitted.

The multi-layer piezoelectric element 5 in the fourth embodiment iscomposed of twelve piezoelectric element films L1 to L12, as shown inFIG. 14A. On the piezoelectric element films L1 to L12, there are formedelectrode films P1 to P4 and via-hole electrodes H1 to H4, in the sameway as described in the preceding embodiments.

The electrode films P1 and P2 formed on each of the piezoelectricelement films L2, L4 and L6 and the electrode film P3 formed on each ofthe piezoelectric element films L3, L5 and L7 make the piezoelectricelement films L2 to L6 have areas R1 and R2, as shown in FIG. 14B. Suchareas R1 and R2 function only as those for exciting the vibration inMODE-A.

Also, the electrode film P4 formed on each of the piezoelectric elementfilms L8, L10 and L12 and the electrode film P3 formed on each of thepiezoelectric element films L7, L9 and L11 make the piezoelectricelement films L7 to L11 have an area R3, as shown in FIG. 14B.

The potential states of the electrode films P1 to P4 obtained when, withthe via-hole electrode H3 set as a common potential, a positivepotential is applied to the via-hole electrodes H1 and H4 and a negativepotential is applied to the via-hole electrode H2 are represented bycharacters (+), (−) and (GND) shown in FIG. 14A. Such a state aspolarized in the above-described manner is schematically indicated byarrows in FIG. 14B. As shown in FIG. 14B, the areas R1 and R2 arepolarized in opposite directions.

When the multi-layer piezoelectric element 5 having the above-describedconstruction is incorporated into the vibration element 1, the areas R1and R2 are arranged not to include the neutral plane T1 shown in FIGS.2A and 2B and are located on one side of the neutral plane T1. The areaR3 is arranged not to include the neutral plane T2 and are located onone side of the neutral plane T2.

The vibration state obtained when the multi-layer piezoelectric element5 in the fourth embodiment is incorporated into the vibration element 1is described. As in the preceding embodiments, potentials V1 to V4 areapplied to the terminal electrodes H1 to H4, respectively. The terminalelectrodes H1 to H4 function also as via-hole electrodes H1 to H4,respectively, formed on each piezoelectric element film.

It is now assumed that the potential difference between the potentialsV1 and V3 is E1, the potential difference between the potentials V2 andV3 is E2, and the potential difference between the potentials V4 and V3is E3.

First, the excitation of the vibration in MODE-A (being the same as inthe first embodiment) in the vibration element 1 is described. With theelectrical conduction effected and the driving signals determined insuch a manner that the potential difference E1 becomes equal to thepotential difference E2, strains in opposite directions are caused atthe areas R1 and R2, respectively. In this instance, an exciting forcecorresponding to the potential difference E3 is generated in the areaR3, but the area R3 does not operate as an exciting force in MODE-A.

In other words, the vibration in MODE-A is excited with the areas R1 andR2 operating in a unimorph state as exciting forces.

Also, the vibration in MODE-B (being the same as in the firstembodiment) is excited with the area R3 operating in a unimorph state asan exciting force.

According to the fourth embodiment, the whole of regions constitutingthe vibration element 1 can participate in generating a driving forceonto a driven element (linear slider 6), so that an ultrasonic actuatorhaving compatibility between reduction in size and increase in outputpower can be realized.

(Fifth Embodiment)

FIG. 15 is a perspective view showing the appearance of a vibrationelement 1 in a linear-type ultrasonic actuator serving as avibration-type driving device according to a fifth embodiment of theinvention. In FIG. 15, the vibration element 1 is constructed with athin plate formed into an approximately rectangular shape. On one endsurface of the vibration element 1, there are disposed four protrudingportions 3-1 to 3-4. Then, on the tips of the protruding portions 3-1 to3-4, there are formed contact portions 4-1 to 4-4, respectively, whichare kept in contact with a driven element (not shown).

Further, the vibration element 1 is composed of a piezoelectric element5 formed into an approximately rectangular shape and a driving plate 2on which the protruding portions 3-1 to 3-4 are formed integrallytherewith. The vibration element 1 is arranged such that vibrations areexcited in two flexural vibration modes (MODE-A and MODE-B), as shown inFIGS. 16A and 16B.

MODE-A is a secondary out-of-plane flexural vibration mode in whichnodes are generated at three points along the X direction, as shown inFIG. 16A, and MODE-B is a tertiary out-of-plane flexural vibration modein which nodes are generated at four points along the Y direction, asshown in FIG. 16B. Each of the protruding portions 3-1 to 3-4 isdisposed in the vicinity of a position where a node in MODE-A isgenerated and an antinode in MODE-B is generated.

The vibration in MODE-A causes a reciprocating motion in the X directionto be generated at the protruding portions 3-1 to 3-4, and the vibrationin MODE-B causes a reciprocating motion in the Z direction to begenerated at the protruding portions 3-1 to 3-4. Then, vibrations in thetwo vibration modes (MODE-A and MODE-B) are excited in such a way as tomake an adequate relation of phases thereof, so that an ellipticalmovement can be generated at the contact portions 4-1 to 4-4.

Here, since each of the protruding portions 3-1 to 3-4 is disposed, asmentioned above, in the position where a node in MODE-A is generated andan antinode in MODE-B is generated, the protruding portions 3-1 to 3-4can be displaced to a large degree both in the X direction and the Zdirection. Accordingly, a large driving force from the vibration element1 can be exerted onto the driven element, so that a high-powervibration-type driving device can be attained.

FIG. 17 shows the arrangement of electrode films of the piezoelectricelement 5 employed in the vibration element 1 according to the fifthembodiment. On one end surface of the piezoelectric element 5, there areformed six electrode films P1 to P6. In the piezoelectric element 5,areas R1 to R6 are formed corresponding to the electrode films P1 to P6,in the same way as described in the foregoing.

The areas R1 and R4 as well as the areas R2 and R5 and the areas R3 andR6 are so disposed as to be symmetric with respect to the Y-axis passingthrough the center of the piezoelectric element 5. Further, the areas R1to R3 as well as the areas R4 to R6 are so disposed as to be aligned inthe Y direction.

The areas R1 to R6 are polarized in the thickness direction of thepiezoelectric element 5. In FIG. 17, characters (+) and (−) are used forindicating the individual polarized states of the areas R1 to R6.

The action of the vibration element 1 in which the above-mentionedpiezoelectric element 5 is used is described.

First, a common driving signal V1 is supplied to the areas R1 to R3, andanother common driving signal V2 is supplied to the areas R4 to R6.

When the driving signal V1 coincides with the driving signal V2 both inwaveform and phase, the vibration in MODE-B is excited in the vibrationelement 1. Also, when the driving signal V1 coincides with the drivingsignal V2 in waveform but the driving signal V1 differs from the drivingsignal V2 in phase by 180 degrees or thereabout, the vibration in MODE-Ais excited in the vibration element 1.

When the driving signal V1 coincides with the driving signal V2 inwaveform but the driving signal V1 differs from the driving signal V2 inphase relatively by 90 degrees, the vibrations in MODE-A and MODE-B areexcited in the vibration element 1 with the phase difference of 90degrees maintained relatively.

As a result, elliptical movements in the same direction are generated atthe contact portions 4-1 to 4-4. The loci of such elliptical movementsare in the same shape at the contact portions 4-1 to 4-4, and thetemporal phases of the elliptical movements become different from eachother by 180 degrees between the contact portions 4-1, 4-2 and thecontact portions 4-3, 4-4.

In the vibration-type driving device according to the fifth embodiment,a plurality of protruding portions 3-1 to 3-4 are disposed and aplurality of contact portions 4-1 to 4-4 are formed. Accordingly, thecontact area between the driven element and the vibration element 1 canbe increased as much as the increased number of protruding portions, sothat the transmission of a driving force between the driven element andthe vibration element 1 can be ensured more reliably.

(Sixth Embodiment)

In the above-described vibration element, there is required apiezoelectric element having respective dedicated electrodes forexciting vibrations in a plurality of vibration modes in the vibrationelement. Therefore, it is necessary to use a piezoelectric elementhaving a complicated electrode pattern or to use a multi-layerpiezoelectric element composed of a plurality of piezoelectric elementsjoined one upon another. Further, since directions of polarizationdiffer with individual electrode patterns, the process of polarizationbecomes complicated.

In a sixth embodiment and subsequent embodiments of the invention, afurther-improved vibration element in which an electro-mechanical energyconversion element is made to have a simplified electrode pattern isdescribed.

FIG. 18 is a perspective view showing the appearance of a vibrationelement 1 in a linear-type ultrasonic actuator serving as avibration-type driving device according to the sixth embodiment of theinvention. In FIG. 18, there are shown a driving plate 2 composed of anelastic body made of metal and formed into a rectangular plate shape, apiezoelectric element (electro-mechanical energy conversion element) 5bonded to the back side of the driving plate 2, and protruding portions3 provided on the top surface of the driving plate 2.

The protruding portions 3 is arranged to be kept in contact with adriven element (an element to be driven), as is described later. Here,on each of the protruding portions 3, a contact portion that excels infriction factor or abrasion resistance may be provided. Further, theprotruding portions 3 may be formed integrally with the driving plate 2by means of press working or the like, or may be formed separately fromthe driving plate 2 and then fixed to the driving plate 2.

If the protruding portions 3 and the driving plate 2 are formedintegrally, the number of steps of assembly work of the vibrationelement 1 can be reduced, and precision fluctuations in individual partscan be avoided because of positioning of parts (the protruding portions3) being unnecessary.

In the vibration element 1 according to the sixth embodiment, vibrationsin two flexural vibration modes can be excited, as described later, andthe two flexural vibration modes are combined to generate an ellipticalmovement at the tips of the protruding portions 3.

Here, the shape of the vibration element 1 is determined in such amanner that the respective resonance frequencies of the above-mentionedtwo flexural vibration modes approximately coincide with each other.More specifically, the respective resonance frequencies of the twoflexural vibration modes can be made to coincide with each other, byappropriately setting the size in the longitudinal direction (longerside) of the driving plate 2 and the size in the direction perpendicularto the longitudinal direction (shorter side) thereof.

The two flexural vibration modes that are caused in the vibrationelement 1 is described below.

FIGS. 19A and 19B are diagrams illustrating the two flexural vibrationmodes. As will be understood from FIGS. 19A and 19B, the vibrationelement 1 of the ultrasonic actuator according to the sixth embodimenthas the same vibration modes as those of the vibration element in thefirst embodiment shown in FIGS. 2A and 2B.

Here, if two protruding portions 3 are disposed symmetrically withrespect to the X-Z plane or the Y-Z plane passing through the center ofthe driving plate 2, the vibration element 1 can impartially receive areaction force from the slider 6 (see FIG. 20) at the protrudingportions 3. Further, since the positional relationship between theslider 6 and the protruding portions 3 becomes stable, it is possible tostabilize an output power of the vibration element 1 without beinginfluenced by changes of environment, load, or the like.

When vibrations in MODE-A and MODE-B as described above are generatedwith a predetermined phase difference, an elliptical movement can begenerated at the tips of the protruding portions 3. The slider 6, whichis a driven element, is arranged to be kept in pressure contact with thetips of the protruding portions 3, as shown in FIG. 20. Accordingly, theslider 6 can be moved in the direction of arrow L in response to theelliptical movement of the protruding portions 3.

FIG. 21 is a diagram showing an electrode pattern of the piezoelectricelement according to the sixth embodiment. In FIG. 21, on thepiezoelectric element 5, there are formed electrode areas that areobtained by division into two equal parts in the longitudinal direction(X direction) of the piezoelectric element 5. Further, the directions ofpolarization in the respective electrode areas are the same (+direction).

To the electrode area located on the right side in FIG. 21 in twoelectrode areas of the piezoelectric element 5, an alternating voltage(V1) is applied, and to the electrode area located on the left side, analternating voltage (V2) is applied.

In FIG. 21, assuming that V1 and V2 are alternating voltages having thefrequency in the vicinity of the resonance frequency in MODE-A andhaving the respective phases different by 180°, at a certain moment, apiezoelectric element part in the right-side electrode area contractsand a piezoelectric element part in the left-side electrode areaexpands. Also, at a different moment, the reverse relation betweencontraction and expansion is obtained. As a result, the vibration inMODE-A is generated in the vibration element 1.

Further, assuming that V1 and V2 are alternating voltages having thefrequency in the vicinity of the resonance frequency in MODE-B andhaving the same phase, the whole piezoelectric element (two electrodeareas) expands at a certain moment and contracts at a different moment.As a result, the vibration in MODE-B is generated in the vibrationelement 1.

In addition, the direction of polarization in one electrode area of thetwo electrode areas is set to the (+) direction and the direction ofpolarization in the other electrode area is set to the (−) direction.

In that event, the vibration in MODE-A can be generated in the vibrationelement 1 by applying, to the two electrode areas, alternating voltages(V1 and V2) having the frequency in the vicinity of the resonancefrequency in MODE-A and having the same phase. Also, the vibration inMODE-B can be generated in the vibration element 1 by applying, to thetwo electrode areas, alternating voltages (V1 and V2) having thefrequency in the vicinity of the resonance frequency in MODE-B andhaving the respective phases different by 180°.

Here, the relationship between the voltages V1 and V2 and the vibrationmodes MODE-A and MODE-B is described with reference to FIG. 22.

In accordance with the description using FIG. 21 as mentioned above, acombination of vectors of V1 and −V2 becomes a vector representingMODE-A, and a combination of vectors of V1 and V2 becomes a vectorrepresenting MODE-B. Here, assuming that the amplitudes of V1 and V2(magnitudes of vectors of V1 and V2) are the same and the phasedifference between V1 and V2 is a phase difference θ between 0° and180°(0°<θ<180°), it is understood that vectors of (V1+V2) and (V1−V2)are orthogonal, as shown in FIG. 22.

This implies that the vibrations in MODE-A and MODE-B are generatedsimultaneously and the phase difference thereof is 90°. As a result, anelliptical movement can be generated at the protruding portions 3 on thedriving plate 2, so that the slider 6, which is kept in contact with theprotruding portions 3, can be driven.

In other words, if the voltage amplitudes of V1 and V2 are made the sameand the phase difference θ between V1 and V2 is made other than 0° and180°, the vibrations in MODE-A and MODE-B can be generatedsimultaneously and the phase difference thereof becomes either 90° or−90°. Further, if the phase difference θ between V1 and V2 is changed,the amplitudes of vibrations in MODE-A and MODE-B can be changed.

As has been described above, even in the vibration element 1 using sucha piezoelectric element 5 that has a simple construction in which anelectrode pattern thereof is divided into two equal electrode areas inthe longitudinal direction of the vibration element 1 and the directionsof polarization of the respective electrode areas are the same, anelliptical movement can be generated at the protruding portions 3 of thevibration element 1.

With the electrode pattern having such a simple construction, thearrangement of wires connected to the electrode areas can be simplified.Further, with the directions of polarization made the same over theentire area of the piezoelectric element, the process is easier ascompared with a piezoelectric element having different directions ofpolarization, and, since the rigidity of the piezoelectric element inthe vicinity of the boundary of electrode areas becomes uniform, idealvibrations can be generated.

Moreover, with the two flexural vibration modes used for the driving ofthe driven element, the vibration-type driving device can be reducedwhile preventing natural frequencies from increasing, as compared withanother vibration-type driving device that drives a driven element bymeans of a combination of flexural vibration and longitudinal vibration.

Although not discussed, it should be noted that the invention is notlimited to combination of a secondary flexural vibration mode (MODE-A)and a primary flexural vibration mode (MODE-B) to drive the drivenelement.

More specifically, any kind of flexural vibration mode (a flexuralvibration mode of different order) may be used as long as an ellipticalmovement can be generated by the combination of a mode that is causedwhen alternating voltages having a phase difference of 0° are applied asV1 and V2 and a mode that is caused when alternating voltages having aphase difference of 180° are applied as V1 and V2.

Also, it should be noted that the layout and number of protrudingportions 3 might be adequately set. For example, one protruding portion3 may be provided on the center of the driving plate 2 as shown in FIG.23, or four protruding portions 3 may be provided on the driving plate 2as shown in FIG. 25.

In the vibration element 1 shown in FIG. 23, the protruding portion 3makes a reciprocating motion in the X direction as shown in FIG. 24A inresponse to the vibration in MODE-A, and makes a reciprocating motion inthe Z direction as shown in FIG. 24B in response to the vibration inMODE-B. Then, the vibrations in MODE-A and MODE-B are combined togenerate an elliptical movement at the tip of the protruding portion 3,so that the slider 6 is moved in the direction of arrow L.

Here, since the protruding portion 3 is disposed in the vicinity of aposition where a node in MODE-A is generated and an antinode in MODE-Bis generated, the degrees of displacement of the protruding portion 3both in the X direction and the Z direction become large, so that alarger driving force can be exerted on the slider 6.

Also, in the vibration element 1 shown in FIG. 25, the protrudingportions 3 each make a reciprocating motion in the X direction as shownin FIG. 26A in response to the vibration in MODE-A, and make areciprocating motion in the Z direction as shown in FIG. 26B in responseto the vibration in MODE-B. Then, the vibrations in MODE-A and MODE-Bare combined to generate an elliptical movement at the tips of theprotruding portions 3, so that a driven element (not shown) that is keptin contact with the protruding portions 3 is driven in the Y direction.

Here, since each of the four protruding portions 3 is disposed in thevicinity of a position where a node in MODE-A is generated and anantinode in MODE-B is generated, the degrees of displacement of theprotruding portions 3 both in the X direction and the Z direction becomelarge.

Further, while, in the sixth embodiment, the case where a driven element(slider 6) formed into a bar shape as shown in FIG. 20 is kept incontact with the protruding portions 3 has been described, the inventionis not limited to such a case, and a variety of shapes of drivenelements may be employed.

(Seventh Embodiment)

In a seventh embodiment of the invention, the structural arrangement ofthe vibration-type driving device is similar to that described in thesixth embodiment and is, therefore, omitted from the followingdescription.

In the seventh embodiment, the linear-type ultrasonic actuator of thesixth embodiment is used as a drive source in a lens unit for a videocamera, which is electronic equipment. The sectional view (sectionalview as cut through in a direction perpendicular to the optical axis) ofthe lens unit is shown in FIG. 27.

In FIG. 27, reference numeral 11 denotes a lens barrel. Referencenumeral 12 denotes a lens (photo-taking lens), which is held by a frame13. Reference numeral 14 denotes a shaft, which is used as a guidefunctioning when the lens 12 is moved in the optical-axis direction (adirection perpendicular to the drawing surface of FIG. 27). Here, thelens 12 is movable in the optical-axis direction to change the focallength of a photographic optical system.

Reference numeral 1 denotes a vibration element of the ultrasonicactuator described in the sixth embodiment, in which protruding portions3 thereof are arranged to be kept in contact with a slider 6 provided onthe frame 13.

Reference numerals 14A and 14B denote an encoder scale and a lightprojecting-and-receiving element, respectively, which constitute a knownencoder for detecting the position in the optical-axis direction of thelens 12. In the encoder, the light projecting-and-receiving element 14Bprojects light onto the encoder scale 14A and, then, the lightprojecting-and-receiving element 14B reads reflected light from theencoder scale 14A, thereby detecting positional information of the lens12.

Next, a control method for the ultrasonic actuator is described. FIG. 28is a block diagram illustrating a control apparatus in the seventhembodiment.

In FIG. 28, reference numeral 10 denotes an ultrasonic actuator servingas a vibration-type driving device. Positional information of the lens12, which is driven by the ultrasonic actuator 10, is detected by theencoder (the encoder scale 14A and the light projecting-and-receivingelement 14B shown in FIG. 27) and is then measured by a position counter17. The positional information of the lens 12 measured by the positioncounter 17 is compared, at a position comparing portion 18, with aposition command as externally input. A comparison result obtained atthe position comparing portion 18 is input to a phase-differenceselecting portion 19 and a frequency determining portion 20. Theposition comparing portion 18, the phase-difference selecting portion 19and the frequency determining portion 20 in combination function as anarithmetic circuit for controlling the driving speed of the ultrasonicactuator 10.

As has been described in the sixth embodiment, if the amplitudes of twoalternating voltages (V1 and V2) to be applied to two electrodes of theultrasonic actuator 10 (piezoelectric element) are made the same and thephase difference θ between the two alternating voltages (V1 and V2) ismade other than 0° and 180°, the vibrations in MODE-A and MODE-B with aphase difference thereof being 90° are generated in the vibrationelement 1.

Here, the magnitude of amplitudes (Aa) and (Ab) of the vibrations inMODE-A and MODE-B respectively are given by equations 1 and 2 below. Theamplitudes are caused when the phase difference θ between the twoalternating voltages (V1 and V2) is an arbitrary value (from 0° to180°).Aa=|2×cos((π−θ)/2)|  (1)Ab=|2×cos(θ/2)|  (2)

FIG. 29 shows the relationship between the vibration amplitudes inMODE-A and MODE-B obtained by the above equations (1) and (2) and thephase difference θ between the two alternating voltages (V1 and V2). InFIG. 29, the abscissa axis indicates the phase difference θ, and theordinate axis indicates the magnitudes of vibration amplitudes in thetwo vibration modes (MODE-A and MODE-B). In addition, a phase differencebetween the vibrations in MODE-A and MODE-B switches between 90° and−90° with the phase difference of 180° between V1 and V2 set as aboundary. In other words, the direction of driving of the driven element(slider 6) is reversed between the two sides (in the + direction and inthe − direction shown in FIG. 29) of the phase difference of 180°between V1 and V2.

Here, the direction of driving of the slider 6 by the ultrasonicactuator is determined by comparing, at the position comparing portion18, the positional information of the lens 12 obtained from the positioncounter 17 with a target position (stopping position) of the lens 12indicated by the externally-input position command. Then, in accordancewith the direction of driving as determined, the phase difference θbetween V1 and V2 is selected at the phase-difference selecting portion19. More specifically, if the direction of driving of the slider 6 isset to the (+) direction, the phase difference θ of V2 from V1 is made90°, and, if the direction of driving is set to the (−) direction, thephase difference θ of V2 from V1 is made 270°.

It should be noted that, although it is possible to drive the lens 12even with a phase difference θ other than 90° and 270°, in the seventhembodiment, 90° and 270°, each of which is a phase difference θ thatcauses the amplitudes of vibrations in MODE-A and MODE-B to be generateduniformly, are selected.

Next, a control method for the driving frequency is described. Therelationship between the driving frequency of an alternating voltage(V1, V2) applied to the ultrasonic actuator 10 and the driving speed isthe same as that in a typical ultrasonic actuator using resonance, andhas such characteristics that, as shown in FIG. 30, with a resonancefrequency (fr) set as a peak, the driving speed decreases moderately onthe higher-frequency side of the resonance frequency (fr) and decreasesrapidly on the lower-frequency side of the resonance frequency (fr).

If the driving speed is controlled with the above-mentionedcharacteristics, the driving control should be accomplished withfrequencies in the frequency range higher than the resonance frequency(fr).

At the position comparing portion 18, a deviation of the currentposition of the lens 12 based on the output of the position counter 17from the externally-input target position is measured. At the frequencydetermining portion 20, if the above-mentioned deviation is large, thedriving frequency is made closer to the resonance frequency (fr),thereby increasing the driving speed. On the other hand, if thedeviation is small, the driving frequency is made further from theresonance frequency (fr) toward the higher-frequency side, therebydecreasing the driving speed.

In addition, the driving control may be arranged such that, if thedeviation of the position of the lens 12 is within a predeterminedrange, the alternating voltages (V1 and V2) are not applied to theultrasonic actuator.

At the driving signal producing circuit 21, two signals (correspondingto V1 and V2) having the phase difference θ selected by thephase-difference selecting portion 19 and having the frequencydetermined by the frequency determining portion 20 are produced. The twodriving signals are stepped up by the step-up circuit 22 to a voltageenabling the ultrasonic actuator to operate.

The alternating voltages (V1 and V2) as stepped up are applied to theultrasonic actuator 10 (piezoelectric element). According to theabove-described construction, a lens unit that the lens 12 is able toquickly move to a target position can be provided.

(Eighth Embodiment)

As noted above, the driving speed is made to change by varying, inaccordance with a difference between the current position of the lens 12and the target position, the frequency of the alternating voltage (V1,V2) to be applied to the ultrasonic actuator serving as a vibration-typedriving device. Further, either 90° or 270° is selected as a phasedifference θ between the applied voltages V1 and V2 in accordance withthe driving direction of a driven element (slider 6).

In that event, an elliptical movement that is generated at theprotruding portions (3 in FIG. 18) of the vibration element comes intosuch a driving state that the ratio of the amplitude in MODE-A, which isthe amplitude in the lateral direction of the elliptical movement, tothe amplitude in MODE-B, which is the amplitude in the longitudinaldirection thereof, does not vary and only the magnitude of each of theamplitudes in MODE-A and MODE-B varies, as shown in FIGS. 31A and 31B.

In the event that it is intended to drive the lens 12 at a lower speed,the above-mentioned driving method described in the seventh embodimentcauses the amplitude in MODE-B to be too small (see FIG. 31B), so thatthe protruding portions 3 might come into contact with the slider 6 atthe lower side of the elliptical movement, i.e., even at the time of amovement in the direction opposite to the driving direction of theslider 6, and a stable low-speed driving operation may be un-obtainable.

An eighth embodiment of the invention is to further improve the seventhembodiment so as to realize a stable low-speed driving operation. Thecontrol method in the eighth embodiment is described below.

It should be noted that, in the eighth embodiment, the construction ofthe ultrasonic actuator is the same as that described in the sixthembodiment, and such an ultrasonic actuator is incorporated into thelens unit described in the seventh embodiment.

In order to drive the ultrasonic actuator stably at a low speed, it isconceivable to make the amplitude in MODE-B, which is the vibration in adirection to push up the slider 6, larger and the amplitude in MDOE-A,which is the vibration in a direction to drive the slider 6, smaller.

For example, if, as shown in FIGS. 32A and 32B, the driving speed of theslider 6 is controlled in such a way as to make the amplitude in MODE-Bunvarying and the amplitude in MODE-A variable, the slider 6 can bestably driven in a wide range from high-speed driving to low-speeddriving.

FIG. 33 is a block diagram illustrating a control apparatus of theeighth embodiment. The control apparatus provides a phase-differencedetermining portion 23 and an amplitude determining portion 24. Thus,the position comparing portion 18, the phase-difference determiningportion 23 and the amplitude determining portion 24 in combinationfunction as an arithmetic circuit for controlling the driving speed ofthe ultrasonic actuator 10. The other features are similar to thosedescribed in the seventh embodiment.

In the eighth embodiment, the frequency of each of the alternatingvoltages (V1 and V2) to be applied to the ultrasonic actuator is fixedto a predetermined frequency about the resonance frequency (fr), and,then, the phase difference θ between V1 and V2 and the amplitude of eachof V1 and V2 are managed so as to control the driving speed.

While, as has been described in the seventh embodiment, the relationshipof the amplitudes in MODE-A and MODE-B to the phase difference θ betweenthe voltages (V1 and V2) to be applied to electrodes of thepiezoelectric element in the ultrasonic actuator becomes such arelationship as shown in FIG. 29, this is true in a case where thevoltage amplitude of each of V1 and V2 is steadied within a range of thephase difference θ from 0° to 180°.

In that case, the amplitude in MODE-B would vary according to the phasedifference θ, as is indicated by a dotted line in FIG. 29. Therefore, inthe eighth embodiment, the amplitude in MODE-B is steadied by varyingthe amplitude of each of the applied voltages (V1 and V2) according tothe phase difference θ.

FIG. 34 shows the behavior of the vibration amplitude obtained when theapplied voltage (V1 and V2) amplitude is varied according to the phasedifference θ between V1 and V2 so that the amplitude in MODE does notvary. Each voltage amplitude on a line connecting the circle marks shownin FIG. 34 is proportional to a reciprocal of the amplitude in MODE-Bshown in FIG. 29 and is used to compensate for variation of theamplitude in MODE-B. More specifically, the voltage amplitude of each ofV1 and V2 is obtained with multiplication by a coefficient (K) obtainedby the following equation (3) according to the phase difference θ:K=|1/(2×cos(θ/2))|  (3)

The individual voltage amplitudes obtained by using equation (3), above,come into such a relationship as represented by circle marks shown inFIG. 34. The voltages having the thus-obtained amplitude are applied totwo electrodes of the piezoelectric element, so that the amplitude inMODE-B becomes a constant amplitude as indicated by a dotted line shownin FIG. 34.

In this instance, the amplitude in MODE-A comes to have suchcharacteristics as to increase with the phase difference θ advancingfrom 0°toward 180° and to decrease with the phase difference θ advancingfrom 180° toward 360°, as indicated by solid lines shown in FIG. 34. Itshould be noted that, like FIG. 29, the driving directions are madeopposite between the right side (the side of the − direction) and theleft side (the side of the + direction) of FIG. 34 with the phasedifference 180° set as a boundary.

In the eighth embodiment, a description of the driving control operationis as follows. First, at the position comparing portion 18, the currentposition of the lens 12 is compared with a target position. At thephase-difference determining portion 23, the driving direction isdetermined on the basis of a result of comparison provided by theposition comparing portion 18, and it is determined whether to set thephase difference θ between V1 and V2 to a value within a range in whichthe phase difference θ is smaller than 180° (the range of the +direction in FIG. 34) or to a value within a range in which the phasedifference θ is larger than 180° (the range of the − direction in FIG.34).

Further, at the phase-difference determining portion 23, the phasedifference θ is determined in such a way as to make the driving speedequal the difference in distance between the current position of thelens 12 and the target position.

For example, if the lens 12 (slider 6) is to be driven in the (+)direction and the driving speed is to be set high, the phase differenceθ is determined to be a large value within the range in which the phasedifference θ is smaller than 180°. If the driving speed is to be setlow, the phase difference θ is determined to be a small value within therange in which the phase difference θ is smaller than 180°. In thisrange, the amplitude in MODE-B is constant and the amplitude in MODE-Aincreases with the phase difference θ advancing from 0° toward 180°, sothat the driving control operation can be stably driven from low-speeddriving up to high-speed driving.

On the other hand, if the lens 12 (slider 6) is to be driven in the (−)direction and the driving speed is to be set to a high speed, the phasedifference θ is determined to be a small value within the range in whichthe phase difference θ is larger than 180°. If the driving speed is tobe set to a low speed, the phase difference θ is determined to be alarge value within the range in which the phase difference θ is largerthan 180°. In the range in which the phase difference θ is larger than180°, the amplitude in MODE-B is constant and the amplitude in MODE-Aincreases with the phase difference θ advancing from 360° toward 180°,so that it is viable to perform the driving control operation stablyfrom low-speed driving up to high-speed driving.

After the phase difference θ is determined at the phase-differencedetermining portion 23, at the amplitude determining portion 24, avoltage amplitude corresponding to the phase difference θ as determined(a value on the line connecting circle marks shown in FIG. 34) isdetermined. The voltage amplitude to be determined may be obtained byusing equation (3) according to the phase difference θ, and,alternatively, may be obtained from data representative of therelationship between a plurality of phase differences θ and a pluralityof voltage amplitudes, which are previously stored in a storage circuit.

Then, data representative of both the value of the phase difference θ asdetermined at the phase-difference determining portion 23 and the valueof the voltage amplitude as determined at the amplitude determiningportion 24 are input and provided to the driving signal producingcircuit 21 to produce a driving signal based on the data input. Thedriving signal is then supplied to the step-up circuit 22, at whichvoltages (V1 and V2) as stepped up are formed and supplied to thepiezoelectric element of the ultrasonic actuator.

In the above-described driving control operation, since the amplitude ofthe vibration in MODE-B, which is a vibration in a direction to push upthe slider 6 among vibrations of the ultrasonic actuator, is made steadyand the amplitude of the vibration in MODE-A is varied, the slider 6 canbe stably driven in a wide range from high-speed driving to low-speeddriving.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it is understood thatvariations and modifications can be effected within the scope of theinvention as described above, and as noted in the appended claims, by aperson of ordinary skill in the art without departing from the scope ofthe invention.

1. A vibration-type driving device comprising: a vibration elementfurther comprising, a driving member and an electro-mechanical energyconversion element having an electrode, wherein the electro-mechanicalenergy conversion element is capable of using a driving signal from theelectrode to displace the driving member; and a driven element incontact with the driving member of said vibration element, wherein saidvibration element uses the driving signal to excite vibrations in afirst and a second flexural vibration mode, wherein the first flexuralvibration mode is capable of generating a node in a direction which isnon-parallel to a direction of node generation by the second flexuralvibration mode.
 2. A vibration-type driving device according to claim 1,wherein the direction of node generation by the first flexural vibrationmode is perpendicular to the direction of node generation by the secondflexural vibration mode.
 3. A vibration-type driving device according toclaim 2, wherein said driving member is composed of a protrusion.
 4. Avibration-type driving device according to claim 2, wherein said drivingmember is disposed in a position where a node in the first flexuralvibration mode is generated and an antinode in the second flexuralvibration mode is generated.
 5. A vibration-type driving deviceaccording to claim 2, wherein said driving member is disposed in thevicinity of a position where a node in the first flexural vibration modeis generated and an antinode in the second flexural vibration mode isgenerated.
 6. A vibration-type driving device according to claim 2,wherein the order of the first flexural vibration mode is aneven-number-th order, and the order of the second flexural vibrationmode is an odd-number-th order.
 7. A vibration-type driving deviceaccording to claim 2, wherein said electro-mechanical energy conversionelement is a piezoelectric element composed of a plurality of layers. 8.A vibration-type driving device according to claim 7, wherein saidpiezoelectric element has a plurality of driving regions that receiverespective different driving signals as externally input, and theplurality of driving regions each are subjected to polarizationtreatment in the thickness direction of said piezoelectric element.
 9. Avibration-type driving device according to claim 7, wherein saidpiezoelectric element has two driving regions to excite vibrations inthe first and second flexural vibration modes, and the two drivingregions are formed in positions into which said piezoelectric element isdivided in the thickness direction thereof and are arranged to generateexcitation forces in opposite directions in response to inputting of thedriving signal.